Dead reckoning back-up navigational system for a drone

ABSTRACT

The heading and range to a recovery area for a drone on a mission are continuously monitored and stored on board the drone. Any failure in the primary navigational system in the drone is detected and the stored heading and stored range are available for comparison with the on-board compass reading of the drone and an on-board air speed integrator for the drone. Any deviation between the drone compass reading and the stored heading is corrected by generation of an error signal to operate the flight controls of the auto-pilot on the drone to steer the drone towards the recovery area. A landing command signal, in turn, is provided only when the integrated air speed equals the stored range. Corrections for wind conditions are automatically included in the stored heading and range information so that accurate dead reckoning back to the recovery area is realizable. A wholly selfcontained means is thus provided for returning a drone to a specified recovery area in the event of failure of its primary navigational system at any point in time during its mission.

[ July 31,1973

[ 1 DEAD RECKONING BACK-UP NAVIGATIONAL SYSTEM FOR A DRONE [75]Inventors: Lowell O. Lykken, Westlake Village;

Erwin E. Schulze, Jr., Placentia, both of Calif.

[73] Assignee: Lear Siegler, Inc., Santa Monica,

Calif.

[22] Filed: June 15, 1972 [21] Appl. No.: 263,155

[52] US. Cl. 244/345 [51] Int. Cl. F42b 15/10, F42b 15/02, F42b 15/32[58] Field of Search 244/3.15, 3.17

[56] References Cited UNITED STATES PATENTS 3,372,890 3/1968 Borgard eta1. 244/317 3,416,752 12/1968 Hembree 244/317 Primary Examiner-BenjaminA. Borchelt Assistant Examiner-Thomas H. Webb Attorney-Pastoriza & KellyThe heading and range to a recovery area for a drone on a mission arecontinuously monitored and stored on board the drone. Any failure in theprimary navigational system in the drone is detected and the storedheading and stored range are available for comparison with the on-boardcompass reading of the drone and an on-board air speed integrator forthe drone. Any deviation between the drone compass reading and thestored heading is corrected by generation of an error signal to operatethe flight controls of the auto-pilot on the drone to steer the dronetowards the recovery area. A landing command signal, in turn, isprovided only when the integrated air speed equals the stored range,Corrections for wind conditions are automatically included in the storedheading and range inlformation so that accurate dead reckoning back tothe recovery area is realizable. A wholly self-contained means is thusprovided for returning a drone to a specified recovery area in the eventof failure of its primary navigational system at any point in timeduring its mission.

ABSTRACT 4 Claims, 2 Drawing Figures NAVlGATlON AND GUIDANCE --AUT9P\LOT-13 .|5 & E Wei. ononz FLT.

1 PR'MARY CONTROL H STEERING svg r gm l6 MA Pas-mono ND I SERVOS mm 42PR i L EXISTING 5 POSITION RECOVERY 45 ST ERING COMM AND ALTITUDESTORAGE wmo M NO 49 DATA CORRECTION PATENTEDN aT ms 3.7491333 R: h sTA wWIND RECOVERY NAv.

STA.3 FIG I AREA NAvlGAT oN AND GUIDIANCE"T\- AUTQPILDT 13 A. 15 r NAv.I? DRDNE FLT. REC. l H PRIMARY CONTROL '4 STEERING r SYSTEM coMMAND iAND PRE-RGGRD I sERvos PROGRAM [4| 42 L J J Ti 43| FAILURE 45 STEERINGTRIGGER H H COMMAND W 22 HEADING 39 24 STORAGE 4 L w HETADING 33REcDvERY r COMPASS AREA E??? HEADING A "46 K32 38 2| 47 LAND f H RGDMMAND EXISTING RANGE A RANGE TO X sToRAGE RECOVERY I COMPARE 3| 48CIRCUIT so I H :NTEGRATDR -37 as 7 LG/AIRSPEED l ALTITUDE sToRAGE f WINDWIND *53 DATA CORRECT'ON 5| ALTI MET ER FIG. 2

DEAD RECKONING BACK-UP NAVIGATIONAL SYSTEM FOR A DRONE This inventionrelates generally to drone operations and more particularly to a back-upnavigational system for automatically returning a drone to a desiredrecovcry area in the event of failure in its primary navigationalsystem.

BACKGROUND OF THE INVENTION Pilotless aircraft or drones areconventionally provided with a guidance and control system includingprimary navigational means for automatically operating the flightcontrols of the drone to cause the drone to fly in accord with a desiredmission; that is, along a particular flight path calculated in advance.Such drones may be used for reconnaissance work, aerial photography, andthe like. Normally, the programmed flight mission will cause the droneto land in a specified recovery area after the mission has beencompleted so that the drone and its on-board equipment can be recovered.

One typical type of primary navigation system would include an on-boardnavigational radio receiver providing position signals indicating theexisting position of the drone at all times in relation to, for example,fixed ground radio stations. Also on board there would be provided apre-recorded flight program unit providing program signals indicatingpre-programmed positions for the drone. A primary computer responsive todevia tions of the position signals from the program signals in turngenerates primary command signals to operate flight controls in thedrone in a manner to correct such deviations. The actual path that thedrone flies will thus correspond to the pre-programmed mission.

In the event of failure of the primary navigation system on board thedrone or in the event of a sudden radio silence from the fixed radionavigation stations, the drone is simply lost. Not only are such lossesexpensive, but the delay in recovering important data or the delayinvolved in sending off a back-up drone can be very serious particularlyin war time.

BRIEFDESCRIPTION OF THE PRESENT INVENTION With the foregoing in mind, itis a primary object of the present invention to provide a completelyselfcontained, on-board navigational system for automatically returningthe drone to a pre-assigned recovery area in the event of any failure inthe primary navigation system or in navigational signals from fixedground radio stations, the back-up system itself being operable undercomplete radio silence.

More particularly, the drone includes heading storage means for storingthe heading to a recovery area and a range storage means for storing therange of the drone from the recovery area, the heading and rangeinformation being available from the navigational receiver in theprimary system and the pre-recorded flight program unit aboard thedrone. Failure trigger means responsive to a failure in the primarynavigational system then actuates the heading storage; means and rangestorage means so that the particular heading and range stored at thepoint of time of the failure accurately depict the heading and range ofthe drone from the recovery area. Simultaneously, an on-board air speedintegrating means is actuated. The on-board compass heading of the droneis compared with the stored heading signal to provide suitable steeringcommand signals to the drone auto pilot and thus head the drone backtowards the recovery area. Simultaneously, the integrated air speed iscompared with the stored range such that when these signals are equal, aland command signal is given to the drone so that a para chute can bedeployed or the drone landed by any other suitable means.

An important feature of the invention includes the modifying of thestored heading signal and stored range signal to correct for existingwind conditions so that greater accuracy is realizable in returning thedrone to the designated recovery area.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of theinvention will be had by now referring to the accompanying drawings inwhich:

FIG. 1 is plan view illustrating a drone on a flight mission from adesignated recovery area useful in explaining the invention; and,

FIG. 2 is a detailed block diagram of the deadreckoning back-upnavigational system for the drone of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, there isillustrated a typical drone or unmanned aircraft 10 in flight from arecovery area 11 along a predetermined flight path 12. In the exampleshown in FIG. 1, the recovery area 11 corresponds to the starting pointfor the drone but it should be understood that any other recovery areafor the drone could be designated.

The primary navigational system for the drone autopilot includes a radioreceiver for navigational signals provided from fixed radio stations.For example, there are shown three such fixed navigation radio stationsdesignated NAV. STA. l, NAV. STA. 2, and NAV. STA. 3. The signals fromthese navigation stations may be LORAN type signals wherein a suitableprimary onboard computer interprets the signals to define an existingposition of the drone at all times. From this information on board thedrone, a continuous indication of the heading H back to the recoveryarea and the range R from the recovery area is always available. Atypical wind velocity and direction is illustrated in FIG. 1 by thearrows W.

The pre-programmed flight unit on board the drone 10 of FIG. 1 willcause the drone to follow a preassigned path by comparing the programmedposition with the existing position as determined by the radio signalsreceived in the navigational receiver aboard the drone. Any deviationsof the existing position from the programmed position will provide errorsignals which control the flight of the drone in :such a manner as tomaintain it on the pro-assigned path. Normally, the flight mission isprogrammed to return the drone to its starting point if such is thedesignated recovery area or to a different selected recovery area at theend of the mission. However, should any failure occur in the primarynavigational system, pro-recorded flight program unit, or in the event aradio silence should occur so that further signals from the fixednavigational radio stations are no longer received, the drone wouldordinarily be lost.

Referring now to FIG. 2, there :is illustrated the primary navigationsystem and the dead reckoning back- More particularly, the primarysystem includes a navigational signal radio receiver 13 and an on-boardprerecorded program unit for the mission designated 14. Existingposition information and pre-recorded flight information are provided onoutlet lines 15 and 16 and compared in a unit 17. The output from theunit 17 may take the form of an error signal indicating any deviation inthe existing position of the drone and the prerecorded programmedposition. This signal is received in a primary computer 18 for providinga steering command signal to the drone flight control system and servosdesignated by the block 19.

The various blocks 13 through 19 described above constitute the typicalprimary navigational system aboard the drone. The remaining blocks onthe drawing constitute the dead reckoning back-up navigational systemfor the drone in accord with the present invention.. This back-up systemderives existing position signals from a branch line 20 passing from thenavigational receiver 13 to an existing position control unit 21.Simultaneously, the selected recovery area is derived through a branchline 22 from the pre-recorded program unit 14 to a recovery area unit23. The existing position signals and the recovery area position signalsare both passed to the computing units 24 and 25. The unit 24 generatesa continuous heading signal defining the heading to the recovery areaand the unit 25 provides a range signal defining the range to therecovery area. These signals are modified by suitable correction signalsto take into account existing wind conditions. Towards this end, thereis illustrated a wind data unit 26 and wind correction signal generator27 for modifying the heading and range signals in the units 24 and 25.

The corrected heading signal from the unit 24 passes to lead 28 to aheading storage means 29 which continuously stores the heading to therecovery area taking into account the existing wind conditions.Similarly, the corrected range from the unit 25 is passed through anoutput lead 30 to a range storage means 31 wherein the range to therecovery area is continuously stored suitably corrected to take intoaccount wind conditions.

An on-board compass means 32 provides the compass heading of the droneand this information is compared with the stored heading signal in theunit 25 as by unit 33 which will provide a difference or error signal toa steering command signal generator 34.

Anon-board integrator 35 for integrating the air speed as provided byindicator 36 in turn provides a range signal for comparison with thestored range in the unit 31. When these signals are equal, a signal isprovided by a comparecircuit 37 to a land command signal generator 38.

The system is completed by the provision of a failure logic trigger unitdesignated by the block 39 is the upper center portion of FIG. 2. Thistrigger unit includes an input line 40 from the navigational receiver13, an input line 41 from the pre-recorded program unit 14, and an inputline 42 from the primary computer steering command unit 18. A failure inany one of these three components will trigger the failure logic block39 to provide an output trigger control signal on line 43. This signalis passed to line 44 to disable or disconnect the primary steeringcommand unit 18 from the drone flight control system and servos 19 anden able or connect up the outputs from the steering command unit 34 andland command unit 38 to the drone flight control system and servos 19.In addition, the trigger circuit is passed through a branch line 45 tothe heading storage means 29 and through branch lines 46 and 47 to therange storage means 31. Also, the same trigger is passed through branchlead 48 to start the integrator 45.

OPERATION In operation, existing position signals and recovery areaposition data are continuously provided by the navigational receiver 13and pre-recorded program unit 14 for the mission to the units 21 and 23and thence to heading and range computer units 24 and 25. The computedheading to the recovery area and range from the recovery area of thedrone at all times are then continuously stored in the heading storagemeans 29 and range storage means 31. So long as the primary navigationalsystem is functioning properly, there is no further action by theback-up system described except to continuously store the recovery areaheading and recovery area range.

Assume now that some type of failure occurs in either the navigationreceiver, pre-recorded program unit, or primary computer system or evenin the navigational radio signals from the fixed ground stations. Inthis event, the failure will be detected by the failure trigger unit 39over one or more of its input lines 40, 41 or 42. An output trigger onthe line 43 will then disconnect the primary steering command unit 18from the drone flight control system 19 and connect the steering command34 and land command unit 38 to the drone flight control system.Simultaneously, the same trigger system will trigger the heading storagemeans 29 and range storage means 31 so that these units provide aconsistent signal indicating the heading and range of the recovery areaat the precise point in time that the failure occured. Since the headingand range are continuously corrected by the wind conditions up to thepoint of failure, the stored heading and range values will accuratelyenable the drone to be returnedto the designated recovery area on theassumption that such wind conditions will remain the same during therecovery period. 7

it will also be recalled that the actuating trigger from the failurelogic trigger circuit 39 is passed through branch line 48 to theintegrator 35 so that the air speed of the drone is integrated from thepoint in time that failure occured.

The actual compass heading of the drone by the onboard compass 32 in theform of a signal is compared with the stored heading signal in thestorage unit means 29 by the comparator 33 and any error or differencein these signals causes the steering command 34 to provide a steeringcommand signal to the drone flight controls to correct the heading. Whenthe compass heading unit 32 corresponds with the stored heading in theunit 29, the steering command signal will become zero and the drone willstay on the particular heading defined by the stored heading signal inthe unit 29.

As the droneheads towards the selected recovery area, the output fromthe air speed integrator 35 will approach a value corresponding to therecovery area range stored in unit 31. The comparator circuit 37generates a signal when the integrated air speed equals the stored rangeto thereby operate the land command unit 38 and trigger suitablemechanism in the drone flight controls to deploy a parachute orotherwise land the drone.

It will be appreciated from the foregoing, that the back-up navigationalsystem is completely selfcontained and does not rely on any externalradio signals or the like in order to return the drone to a selectedrecovery area. The dead reckoning operation is greatly increased inaccuracy as a consequence of the introduction of wind corrections by theunits 26 and 27 in the stored heading and range data.

Thus far, nothing has been mentioned concerning the altitude at whichthe drone flies. However, once an assigned altitude has been initiallyreached, it can be maintained constant and special variable controlssuch as provided for range and heading are not necessary in returningthe drone. On the other hand, if the altitude is programmed to vary anda failure should occur when the drone is at a low altitude, it would bedesirable to return it at a safe higher altitude since the return pathwould normally be a straight line dead-reckoned course usually differentfrom the programmed flight course particularly if the recovery area isdifferent from the starting or launch position.

In the foregoing event, the back-up navigational system could include analtitude storage unit such as indicated at 49 in FIG. 2. This unit isconnected to the prerecorded program unit 14 by lead 50 and monitors andstores the altitude. When failure occurs, the same trigger signal fromthe lead 46 for actuating the range storage unit 31 and integrator 35would trigger the altitude storage unit 49 and if the drone is not at asafe altitude at the time of failure, a proper constant safe altitudesignal will be provided by the unit 49. This signal can then be comparedwith an actual altitude signal from the drone altimeter shown at 51 in adifferential amplifler 52. Any difference in the signal will provide anerror signal on output 53 to the flight control 19 to bring the drone tothe predetermined safe return altitude.

By utilizing the foregoing system on drones, the chances for recoveringdrones in which a failure occurs in the primary navigational system aregreatly increased all to theend that the cost of a new drone and delaysin retrieving valuable information obtained by the drone are avoided.

What is claimed is:

l. A dead reckoning back up navigational system for a drone comprising,in combination:

a. heading storage means for storing the heading to a recovery area;

b. range storage means for storing the range of the drone from therecovery area;

c. on-board compass means providing the existing heading;

d. on-board air speed integrating means; and

e. failure trigger means responsive to a failure in the primarynavigational system to actuate the heading storage means, range storagemeans, and air speed integrating means to thereby provide correctivesteering command signals to the drone flight control system to cause itto head in the direction defined by the stored heading signal at thetime of failure and to land when the integrated air speed equals thestored range at the time of failure,

whereby the drone is automatically returned to the recovery area by deadreckoning.

2. A dead-reckoning back-up navigational system according to claim 1,including wind correction means for modifying the stored heading andrange information to take into account wind conditions existing at thetime of failure.

3. A dead reckoning back-up navigational system for a drone on a flightmission under control of an on board navigational receiver providingposition signals indicating the existing position of the drone at alltimes in relation to fixed ground radio stations, an on-boardpre-recorded flight program unit providing program signals indicatingpre-programmed positions for the drone, and primary means responsive todeviations of the position signals from the program signals forgenerating primary command signals to control the drone flight controlsin a manner to correct the deviations, said dead-reckoning back-upnavigational system including, in combination:

a. means connected to the navigational receiver providing existingposition signals;

b. means connected to the pre-recorded flight program unit providingrecovery area signals;

c. means on the drone providing wind correction signals;

d. heading computer means receiving said existing position signals,recovery area signals, and wind correction signals to generate inresponse thereto a corrected recovery area heading signal;

e. range computer means receiving said existing position signals,recovery area signals, and wind correction signals to generate inresponse thereto a corrected recovery area range signal;

f. heading storage means connected to said heading computer means forcontinuously storing said corrected recovery area heading signal;

g. range storage means connected to said range computer means forcontinuously storing said corrected recovery area range signal;

h. on-board compass means for providing a heading signal of the drone atits existing position;

i. steering command signal means responsive to any differences betweenthe on-board compass heading signal and the stored recovery area headingsignal to provide a correction steering signal;

j. on-board air speed integrating means for providing a range signalindication of the distance the drone has traveled from its existingposition;

k. landing command signal means responsive to said range signal and thestored recovery area range signal to provide a landing command signalwhen the range signal equals the stored recovery area range signal; and,

1. failure trigger means responsive to a failure in the on-boardnavigational receiver, on-board prerecorded flight program unit orprimary means providing primary command signals, to disconnect saidprimary means and activate the heading and range storage means, and thecompass means and air speed integrating means, and connect said steeringcommand signal means and said landing command signal means to the droneflight controls, whereby wholly self-contained control of the drone toreturn it to and land it at the recovery area is provided.

tion altitude signal to the drone flight control system so that thedrone will return to the recovery area at the defined altitude.

1. A dead reckoning back up navigational system for a drone comprising,in combination: a. heading storage means for storing the heading to arecovery area; b. range storage means for storing the range of the dronefrom the recovery area; c. on-board compass means providing the existingheading; d. on-board air speed integrating means; and e. failure triggermeans responsive to a failure in the primary navigational system toactuate the heading storage means, range storage means, and air speedintegrating means to thereby provide corrective steering command signalsto the drone flight control system to cause it to head in the directiondefined by the stored heading signal at the time of failure and to landwhen the integrated air speed equals the stored range at the time offailure, whereby the drone is automatically returned to the recoveryarea by dead reckoning.
 2. A dead-reckoning back-up navigational systemaccording to claim 1, including wind correction means for modifying thestored heading and range information to take into account windconditions existing at the time of failure.
 3. A dead reckoning back-upnavigational system for a drone on a flight mission under control of anon-board navigational receiver providing position signals indicating theexisting position of the drone at all times in relation to fixed groundradio stations, an on-board pre-recorded flight program unit providingprogram signals indicating pre-programmed positions for the drone, andprimary means responsive to deviations of the position signals from theprogram signals for generating primary command signals to control thedrone flight controls in a manner to correct the deviations, saiddead-reckoning back-up navigational system including, in combination: a.means connected to the navigational receiver providing existing positionsignals; b. means connected to the pre-recorded flight program unitproviding recovery area signals; c. means on the drone providing windcorrection signals; d. heading computer means receiving said existingposition signals, recovery area signals, and wind correction signals togenerate in response thereto a corrected recovery area heading signal;e. range computer means receiving said existing position signals,recovery area signals, and wind correction signals to generate inresponse thereto a corrected recovery area range signal; f. headingstorage means connected to said heading computer means for continuouslystoring said corrected recovery area heading signal; g. range storagemeans connected to said range computer means for continuously storingsaid corrected recovery area range signal; h. on-board compass means forproviding a heading signal of The drone at its existing position; i.steering command signal means responsive to any differences between theon-board compass heading signal and the stored recovery area headingsignal to provide a correction steering signal; j. on-board air speedintegrating means for providing a range signal indication of thedistance the drone has traveled from its existing position; k. landingcommand signal means responsive to said range signal and the storedrecovery area range signal to provide a landing command signal when therange signal equals the stored recovery area range signal; and, l.failure trigger means responsive to a failure in the on-boardnavigational receiver, on-board pre-recorded flight program unit orprimary means providing primary command signals, to disconnect saidprimary means and activate the heading and range storage means, and thecompass means and air speed integrating means, and connect said steeringcommand signal means and said landing command signal means to the droneflight controls, whereby wholly self-contained control of the drone toreturn it to and land it at the recovery area is provided.
 4. Adead-reckoning back-up navigational system for a drone according toclaim 3, including an altitude storage unit for defining a safe returnaltitude to the recovery area for comparison and with the actualaltitude of the drone in the event of a failure to provide a correctionaltitude signal to the drone flight control system so that the dronewill return to the recovery area at the defined altitude.